Polyphosphazene membranes. III. Solid-state characterization and properties of sulfonated poly[bis(3-methylphenoxy)phosphazene]

Abstract

Poly[bis(3-methylphenoxy)phosphazene] was sulfonated in a solution with SO 3 and solution-cast into 100 -200-m-thick membranes from N,N-dimethylacetamide. The degree of polymer sulfonation was easily controlled and water-insoluble membranes were fabricated with an ion-exchange capacity (IEC) as high as 2.1 mmol/g. For water-insoluble polymers, there was no evidence of polyphosphazene degradation during sulfonation. The glass transition temperature varied from Ϫ28°C for the base polymer to Ϫ10°C for a sulfonated polymer with an IEC of 2.1 mmol/g. The equilibrium water swelling of membranes at 25°C increased from near zero for a 0.04-mmol/g IEC membrane to 900 % when the IEC was 2.1 mmol/g. When the IEC was Ͻ 1.0 mmol/g, SO 3 attacked the methylphenoxy side chains at the para position, whereas sulfonation occurred at all available aromatic carbons for higher ion-exchange capacities. Differential scanning calorimetry, wide-angle X-ray diffraction, and polarized microscopy showed that the base polymer, poly[bis(3-methylphenoxy)phosphazene], was semicrystalline. For sulfonated polymers with a measurable IEC, the 3-dimensional crystal structure vanished but a 2-dimensional ordered phase was retained.

Ion exchange membranes derived from sulfonated polyaramides

“…4. As it was reported for several sulfonated polymers [35,[37][38][39], the wateruptake by the sulfonated polyamides increases with the content of ionic groups in the polymer backbone. Fig.…”

Sulfonimide Polyphosphazene-Based H[sub 2]/O[sub 2] Fuel Cells

“…Sulfonated poly͑ary-loxyphosphazenes͒ have been investigated as fuel cell membranes by Pintauro and co-workers. [14][15][16] Proton conductivities of the sulfonated poly͑aryloxyphosphazene͒ membranes were about half that of Nafion 117 ͑if the ion exchange capacities of both membranes are similar͒, however, the methanol diffusion coefficients for these membranes were almost an order of magnitude lower than those measured for Nafion. Improvements to the mechanical properties of these membranes were obtained by blending with poly͑vinylidene fluoride͒ ͑PVDF͒.…”

Transport Properties of Polyphosphazenes

“…In the case of sulfonated P3MPP, Tang and co-workers [21] have reported that diffusion coefficients at 251C for methanol concentrations between 1.0 and 5.0 M were in the range 8.0 Â 10 À8 to 4.0 Â 10 À7 cm 2 /s. These are significantly lower than reported for Nafion and therefore offer promise for DMFC applications.…”

“…Several polyphosphazenes have been proposed for use in DMPCs, due to their low methanol crossover compared to Nafion. These include sulfonated alkyl group-substituted polyphosphazenes based on poly[bis(phenoxy)phosphazenes] (5) [21][22][23], such as sulfonated poly[(3-methylphenoxy)(phenoxy)phosphazene] (P3MPP) (6) and sulfonated poly[bis(3-methylphenoxy)phosphazene] (7) (Chart 2). Phosphonated polyphosphazenes [24] have also been used as described below.…”